The current portable electronic devices are almost absolutely dependent on rechargeable lithium secondary battery as their power. This demand drives people to continuously endeavor to various researches to increase the specific capacity and the specific energy, prolong the serving life, and improve the safety.
The safety problem of the lithium secondary battery mainly comes from the raised internal temperature of the battery, including improper heating, overcharge, and short circuit due to contact of the positive electrode material and the negative electrode material. When the internal temperature of the battery is continuously raised and cannot be inhibited, the separator film for separating the positive electrode material and the negative electrode material will be melted and broken, thus resulting in large short-circuit current, and then the battery will get hot at an accelerated rate. When the temperature of the battery is raised to 180° C., decomposition of the electrolyte and the positive electrode material occurs, a large amount of heat is generate and a large amount of gas is emitted, thus causing fire, combustion, explosion, and other dangers.
It can be seen that, the safety of the lithium secondary battery is associated with the reaction temperature of the electrolyte and the positive electrode material and the decomposition voltage of the electrolyte. The higher the reaction temperature of the electrolyte and the positive electrode material is (representing that the high-temperature tolerance is higher), the higher the decomposition voltage of the electrolyte is (representing that the overcharge tolerance is higher), and the better the safety of the lithium secondary battery is. Therefore, to ensure the safe use of the consumer, a non-aqueous electrolyte capable of improving the safety of the lithium secondary battery is deeply desired.